1. Field
The present disclosure generally relates to fabrication of composite laminate structures, and deals more particularly with a method of forming contours in a flat composite ply stack that allows ply slippage during the forming process.
2. Background
When stacking and collating multi-ply composite laminates, it may be desirable to maintain desired ply locations and/or ply orientations in order to meet design requirements. In the case of reinforced laminates using thermoset resins, it may be relatively easy to maintain ply locations and orientations due to the inherent tackiness of thermoset polymers. However, other types of composites, such as reinforced thermoplastic resins, may lack the tackiness of theromsets. Therefore, thermoplastic resin plies may need to be staked or tacked together in order to maintain the desired ply locations and/or orientations during collation and subsequent forming and consolidation processes.
Challenges may arise when forming tacked ply stacks into cross sectional part shapes that are contoured, such as those having tightly radiused corners. Depending on the location of the ply tacks, the tacks may result in ply distortion, buckling and/or wrinkling in the finished part because of the reduced ability of the plies to slip relative to each other during the forming process. Currently, this problem is solved primarily by trial and error placement of the tacks. However, the trial and error approach may be timing consuming, may increase material scrap and may not always be effective in eliminating ply buckling, distortion and/or wrinkling.
Accordingly, there is a need for a method of fabricating contoured composite laminates with ply build-ups using tacked plies that allows ply slippage when a flat composite ply stack is formed into a part having a contoured cross sectional shape. There is also a need for a method of fabricating contoured thermoplastic laminates having ply build-ups that reduces ply buckling, distortion and/or wrinkling.